Electronic devices are generally subject to tests for verifying their correct operation; this is of the utmost importance to ensure a high quality of a production process of the electronic devices. The tests may be performed on each electronic device at different levels of the corresponding production process: for example, a test process being called EWS (Electrical Wafer Sort) is performed on the electronic devices being still within a corresponding wafer of semiconductor material, before they are diced into chips and embedded in corresponding packages. Such test may include a set of measurements being executed on each electronic device by an automatic test apparatus, known as ATE (Automatic Test Equipment). The test apparatus is provided with a probe card, which includes a plurality of probes being made of conductive material for contacting corresponding terminals of the electronic devices to be tested. The probe card is positioned above a group of electronic devices of the wafer so that the probes mechanically contact their terminals (step that technically is called probing); this creates an electrical connection between the test apparatus and the terminals of such electronic devices, which allows their test. The same steps are repeated in succession on each group of electronic devices of the wafer until testing all the electronic devices on it.
Such technique, although widely used, may have some drawbacks. First, the contact between each probe and the corresponding terminal may exhibit an electrical discontinuity being due, for example, to the hardness of the material, to the morphology of the contact surfaces and to the presence of oxides, debris or other organic or inorganic elements. Such electrical discontinuity increases the electrical resistance at the interface of the contact between the probe and the terminal, thereby causing, for example, possible wrong failures resulting in a loss of yield in the production process of the electronic devices.
Moreover, such technique is invasive, since the terminals of the electronic devices to be tested may suffer deteriorations and they may be damaged even irreparably after a certain number of probing operations. These deteriorations cause a loss of electrical continuity between the probes and the terminals, with consequent reliability decrease in case of reiterations of the executed probing and tests. Moreover, since the terminals may also be used after the test to bond the electronic devices with other electronic devices and/or pins of the corresponding packages, the deterioration of the terminals being induced during the probing and the subsequent execution of the tests may cause problems with the bonding itself.
In addition, there are the mechanical limits of the electronic devices of the last generation, which exhibit a high number of terminals having a reduced area and being arranged at close distance to one another. In particular, the reduced area of the terminals may require that a correct alignment and centering over time between the probes of the probe cards and the terminals of the electronic devices should be maintained, so as to avoid the damage of a passivation layer around the terminals that is caused by a probing being not totally accurate, while the close distance to which such terminals are mutually arranged may make it difficult to manufacture the probe cards.
In order to solve some of the above-mentioned drawbacks, it is known to implement a POP (Probe Over Passivation) structure in association with each terminal. Such POP structure includes a metal layer being deposited on the terminal and on part of the passivation layer of the electronic device around the terminal. In such way, by having available a metal layer with a greater area than that of the single terminal, a first portion of such metal layer may be used for the probing during the test, while a second portion of such metal layer may be used for the following bonding. In this way, by separating the area wherein the probing is made from that wherein the bonding will be made, the problem of the deterioration that affects the good quality of the bonding is reduce in severity or eliminated.
However, such solution is not always sufficiently satisfactory, since the making of the probing on a metal layer over the passivation layer may cause structural subsidences of layers under the passivation layer. In any case, it may not solve the problem of the reliability decrease of the test in case of a reiteration thereof.